I spent some time searching and coding simple documents, but failed and therefore I'm asking for help...

A section such as chapter cn have custom keys with values. One uses the: \structureuservariable command to access such values.

How can I use such a value to create a custom header in a format:

Prefix: \structureuservariable{foo}

I am asking for the only thing that worked when I tried was calling the: \setupheadertexts command inside a chapter environment block with some prefix. Unfortunately the value from the custom field was not expanded.

It was correctly inserted in a regular paragraph.

For example:

\startchapter

[title={A sample title}][custom_something={random_value}]

...

\stopchapter

How can I put the value of: custom_something in the header with some prefix?

All the best and thanks,

Pawel